One of the major triggers of relapse among patients recovering from substance use disorders is exposure to stressful or traumatic events. In animal models of drug-seeking behaviors including conditioned place preference (CPP), exposure to a stressor, including forced swim or social defeat stress (SDS), results in significant reinstatement of an extinguished cocaine-induced CPP. SDS- but not cocaine-primed reinstatement depends on activation of kappa opioid receptors (KORs) located on the serotonergic neurons of the dorsal raphe nucleus (DRN). However, it remains unknown what upstream, cortical areas are responsible for controlling the DRN during expression of stress-induced reinstatement of drug-seeking behavior. Interestingly, the DRN possesses a number of direct inputs from KOR-expressing regions of the prefrontal cortex (PFC)-an area previously found to play an important role in stress and drug-seeking behavior. This proposal therefore aims to identify and characterize the involvement of cortical-KORs in mediating reinstatement of cocaine- seeking behavior in hopes of better understanding the therapeutic potential of the KOR system. Using a combination of retrograde tract tracing, Fos, and KOR immunohistochemistry, Specific Aim 1 will first identify the cortical regions, and KOR activity within these regions, that are responsibe for controlling DRN activity during reinstatement of cocaine-CPP induced by social-defeat stress (SDS). Additionally, Aim 1 will identify the involvement of KORs on the known subset of PFC neurons that simultaneously project to the DRN and ventral tegmental area in reinstatement of CPP. Specific Aim 2 will then directly manipulate KOR activity within these connections to determine a causal role of cortical-KORs in reinstatement of cocaine-CPP. Using site- and connection-specific viral-mediated re-expression of KORs, the experiments of Aim 2 will assess the ability of KOR re-expression in the DRN and on DRN-projecting PFC neurons to rescue a deficit in SDS- reinstatement exhibited by KOR-KO mice. This proposal requires extensive training in molecular, genetic, biochemical and behavioral techniques, and the results of these experiments will provide unique insight into the involvement of the cortical and subcortical KOR systems in regulating stress-induced reinstatement of cocaine-CPP. Overall, these experiments are intended to further our understanding of how the KOR system is involved in the convergence of the stress and reward pathways that is required for expression of stress- induced relapse.